Tag Archives: Habitable

Polemics

Jupiter deflects comets and asteroids that might otherwise hit Earth

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Circumstellar Habitable Zone
Circumstellar Habitable Zone

This is an older article from Astrobiology magazine, but it shows how important Jupiter is for habitability.

Excerpt:

To a biologist, the ingredients needed to form life include water, heat and organic chemicals. But some in the astrophysics and astronomy community argue that life, at least advanced life, may require an additional component: a Jupiter-sized planet in the solar neighborhood.

“A long-period Jupiter may be a prerequisite for advanced life,” said Dr. Alan Boss, a researcher in planetary formation. Boss, who works at the Carnegie Institution of Washington, is a member of the NASA Astrobiology Institute (NAI).

In our own solar system, Jupiter, with its enormous gravitational field, plays an important protective role. By deflecting comets and asteroids that might otherwise hit Earth, Jupiter has helped to create a more stable environment for life to evolve here. It’s generally believed that a massive impact was responsible 65 million years ago for wiping out dinosaurs on Earth. If not for Jupiter, it’s possible that many other such impacts would have occurred throughout Earth’s history, preventing advanced life from ever gaining a foothold.

Jupiter is significant not only for its size but also for its location in our solar system, far from the Sun. Because it orbits at slightly more than 5 AU (astronomical units the distance between the Earth and the Sun is 1 AU), there is plenty of room in the inner part of our Solar System to accommodate a range of smaller planets.

Within the inner solar system there exists a region, known as the habitable zone, where liquid water, and therefore life, can potentially exist on a planet’s surface. Without liquid water, life as we know it is not possible. The habitable zone around our Sun stretches roughly from the orbit of Venus to the orbit of Mars. Venus is generally believed to be too hot to support life. Earth, it appears, is just right. And the jury is still out on Mars.

Understanding the role that Jupiter plays in our own Solar System helps astronomers focus their search for habitable planets around other stars. “If,” Boss explains, “a Jupiter-mass planet on a stable, circular orbit [around another star at] around 4 to 5 AU was found, without any evidence for other gas giant planets with shorter period orbits, such a discovery would be like a neon light in the cosmos pointed toward that star, saying ‘Look here!’. That star would be a prime target for looking for a habitable, Earth-like planet.”

Previously, I blogged about how the circular orbit of Saturn and the mass of our star also play a role in making our planet habitable.

People who are not curious about science sort of take these blessings for granted and push away the God who is responsible for the clever life-permitting design of our habitat. In contrast, theists are curious and excited about what science tells us about the Creator. Theists care about science, but naturalists have to sort of keep experimental science at arm’s length – away from the presuppositions and assumptions that allow them to have autonomy to live life without respect, accountability and gratitude. Naturalists take refuge in the relief provided by speculative science and science fiction. They like to listen to their leaders speculate about speculative theories, and willingly buy up books by snarky speculators who think that nothing is really something (Krauss), or who think that the cosmic fine-tuning is not real (Stenger), or who think that silicon-based life is a viable scenario (Rosenberg), etc. But theists prefer actual science. Truth matters to us, and we willingly adjust our behavior to fit the scientific facts.

UPDATE: Rebuttal to me here at The Secular Outpost.

News

New study: gamma ray bursts make life impossible in 90% of galaxies

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Galactic Habitable Zone
Galactic Habitable Zone

When you argue for theism from science, you typically use arguments like these:

  • the origin of the universe from nothing (the Big Bang)
  • the fine-tuning of cosmic constants and quantities
  • the origin of the first living cell
  • the sudden origin of animal phyla in the Cambrian explosion
  • the fine-tuning of the galaxy for complex, embodied mind
  • the fine-tuning of the solar system for complex, embodied mind
  • the fine-tuning of the planet (and moon)  for complex, embodied mind

This is a peer-reviewed article from Science, one of the most prestigious peer-reviewed journals. It speaks to the fine-tuning of the galaxy for life.

The article says:

Of the estimated 100 billion galaxies in the observable universe, only one in 10 can support complex life like that on Earth, a pair of astrophysicists argues. Everywhere else, stellar explosions known as gamma ray bursts would regularly wipe out any life forms more elaborate than microbes. The detonations also kept the universe lifeless for billions of years after the big bang, the researchers say.

[…]Astrophysicists once thought gamma ray bursts would be most common in regions of galaxies where stars are forming rapidly from gas clouds. But recent data show that the picture is more complex: Long bursts occur mainly in star-forming regions with relatively low levels of elements heavier than hydrogen and helium—low in “metallicity,” in astronomers’ jargon.

Using the average metallicity and the rough distribution of stars in our Milky Way galaxy, Piran and Jimenez estimate the rates for long and short bursts across the galaxy. They find that the more-energetic long bursts are the real killers and that the chance Earth has been exposed to a lethal blast in the past billion years is about 50%. Some astrophysicists have suggested a gamma ray burst may have caused the Ordovician extinction, a global cataclysm about 450 million years ago that wiped out 80% of Earth’s species, Piran notes.

The researchers then estimate how badly a planet would get fried in different parts of the galaxy. The sheer density of stars in the middle of the galaxy ensures that planets within about 6500 light-years of the galactic center have a greater than 95% chance of having suffered a lethal gamma ray blast in the last billion years, they find. Generally, they conclude, life is possible only in the outer regions of large galaxies. (Our own solar system is about 27,000 light-years from the center.)

Things are even bleaker in other galaxies, the researchers report. Compared with the Milky Way, most galaxies are small and low in metallicity. As a result, 90% of them should have too many long gamma ray bursts to sustain life, they argue. What’s more, for about 5 billion years after the big bang, all galaxies were like that, so long gamma ray bursts would have made life impossible anywhere.

But are 90% of the galaxies barren? That may be going too far, Thomas says. The radiation exposures Piran and Jimenez talk about would do great damage, but they likely wouldn’t snuff out every microbe, he contends. “Completely wiping out life?” he says. “Maybe not.” But Piran says the real issue is the existence of life with the potential for intelligence. “It’s almost certain that bacteria and lower forms of life could survive such an event,” he acknowledges. “But [for more complex life] it would be like hitting a reset button. You’d have to start over from scratch.”

The analysis could have practical implications for the search for life on other planets, Piran says. For decades, scientists with the SETI Institute in Mountain View, California, have used radio telescopes to search for signals from intelligent life on planets around distant stars. But SETI researchers are looking mostly toward the center of the Milky Way, where the stars are more abundant, Piran says. That’s precisely where gamma ray bursts may make intelligent life impossible, he says: “We are saying maybe you should look in the exact opposite direction.”

You need to be able to pick up enough heavy elements from surrounding supernovae to make a metal-rich star, but you have to be far enough away from other stars to avoid getting blasted with gamma rays. The metal-rich star is needed to be able to support the circumstellar habitable zone, which is the zone where liquid water exists on the planet’s surface.

It’s important to understand that this factor in the study just a few of the things you need in order to get a planet that supports life. The more factors you add, the more unexpected complex, embodied life of any kind becomes.

Here are a few of the more well-known ones:

  • a solar system with a single massive Sun than can serve as a long-lived, stable source of energy
  • a terrestrial planet (non-gaseous)
  • the planet must be the right distance from the sun in order to preserve liquid water at the surface – if it’s too close, the water is burnt off in a runaway greenhouse effect, if it’s too far, the water is permanently frozen in a runaway glaciation
  • the solar system must be placed at the right place in the galaxy – not too near dangerous radiation, but close enough to other stars to be able to absorb heavy elements after neighboring stars die
  • a moon of sufficient mass to stabilize the tilt of the planet’s rotation
  • plate tectonics
  • an oxygen-rich atmosphere
  • a sweeper planet to deflect comets, etc.
  • planetary neighbors must have non-eccentric orbits

There’s a good video on the galactic habitable zone for you to watch right here:

It takes a lot to make just one planet that can support complex, embodied life of any kind.

News

Harvard astrophysicist backs the Rare Earth hypothesis

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What is the Rare Earth hypothesis?

It’s the thesis of a recent book written by two scientists at the University of Washington.

Here’s the blurb:

What determines whether complex life will arise on a planet? How frequent is life in the Universe?

In this exciting new book, distinguished paleontologist Peter D. Ward and noted astronomer Donald Brownlee team up to give us a fascinating synthesis of what’s now known about the rise of life on Earth and how it sheds light on possibilities for organic life forms elsewhere in the Universe.

Life, Ward and Brownlee assert, is paradoxically both very common and almost nowhere. The conditions that foster the beginnings of life in our galaxy are plentiful. But contrary to the usual assumption that if alien life exists, it’s bound to be intelligent, the authors contend that the kind of complex life we find on Earth is unlikely to exist anywhere else; indeed it is probably unique to our planet.

With broad expertise and wonderful descriptive imagery, the authors give us a compelling argument, a splendid introduction to the emerging field of astrobiology, and a lively discussion of the remarkable findings that are being generated by new research. We learn not only about the extraordinary creatures living in conditions once though inimical to life and the latest evidence of early life on Earth, but also about the discoveries of extrasolar planets, the parts Jupiter and the Moon have played in our survival, and even the crucial role of continental drift in our existence.

Insightful, well-written, and at the cutting edge of modern scientific investigation, Rare Earth should interest anyone who wants to know about life elsewhere and gain a fresh perspective on life at home which, if the authors are right, is even more precious than we may ever have imagined.

And here’s a review by Library Journal:

“Renowned paleontologist Ward (Univ. of Washington), who has authored numerous books and articles, and Brownlee, a noted astronomer who has also researched extraterrestrial materials, combine their interests, research, and collaborative thoughts to present a startling new hypothesis: bacterial life forms may be in many galaxies, but complex life forms, like those that have evolved on Earth, are rare in the universe. Ward and Brownlee attribute Earth’s evolutionary achievements to the following critical factors: our optimal distance from the sun, the positive effects of the moon’s gravity on our climate, plate tectonics and continental drift, the right types of metals and elements, ample liquid water, maintainance of the correct amount of internal heat to keep surface temperatures within a habitable range, and a gaseous planet the size of Jupiter to shield Earth from catastrophic meteoric bombardment. Arguing that complex life is a rare event in the universe, this compelling book magnifies the significance — and tragedy — of species extinction. Highly recommended for all public and academic libraries.”

Note that Peter Ward is a militant atheist (he has debated against Stephen C. Meyer), and Donald Brownlee is an agnostic. These are not Christians, nor are they even theists. However, I have the book, I have read the book, and I recommend the book. I usually have this book on my shelf at work for show-and-tell.

Now for the latest news about the hypothesis of the book. (H/T Brian Auten of Apologetics 315)

There are always going to be optimistic predictions by scientists who need to attract research funding, but those are hopes and speculations. The data we have today says Earth is rare. The number of conditions required for complex life of any kind is too high for us to be optimistic about alien life in this galaxy, at least. And as the number of requirements for life roll in, the odds of finding alien life that can contact us get slimmer and slimmer.

From the UK Daily Mail. (H/T Peter S. Williams)

Excerpt:

Dr Howard Smith, a senior astrophysicist at Harvard University, believes there is very little hope of discovering aliens and, even if we did, it would be almost impossible to make contact.

So far astronomers have discovered a total of 500 planets in distant solar systems – known as extrasolar systems – although they believe billions of others exist.

But Dr Smith points out that many of these planets are either too close to their sun or too far away, meaning their surface temperatures are so extreme they could not support life.

Others have unusual orbits which cause vast temperature variations making it impossible for water to exist as a liquid – an essential element for life.

Dr Smith said: ‘We have found that most other planets and solar systems are wildly different from our own.

‘They are very hostile to life as we know it.’

‘The new information we are getting suggests we could effectively be alone in the universe.

‘There are very few solar systems or planets like ours. It means it is highly unlikely there are any planets with intelligent life close enough for us to make contact.’ But his controversial suggestions contradict other leading scientists – who have claimed aliens almost certainly exist.

These arguments are actually quite useful, and I include them in my standard list of scientific arguments for theism. (See below) You have to know this stuff cold. Most people believe in aliens because they watched movies made by artists. As a result, they think that humans are nothing special and that God is not interested in us in particular. Which is very convenient for them, because it means they can do whatever they want and not care what God thinks about what they are doing. If you want to defend against the idea that humans are nothing special, and that we were not placed here for a purpose, and that we are not accountable and obligated to seek and know the Creator/Designer, then you’ll need more than feelings. You’ll need science. You’ll need the best science available.

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